During the 10-week stretch from mid-August through October, the most powerful storms tend to form in the Atlantic, Caribbean and Gulf of Mexico. It's also when South Florida is most likely to be struck.

"Almost all South Florida hurricanes and the vast majority of tropical storms have struck our area during these months," said meteorologist Robert Molleda of the National Weather Service in Miami.

Normally, ocean waters heat up and wind shear eases during the heart of the season, allowing tropical systems to form and grow.

The good news this year: Tropical waters should remain cooler than normal and wind shear stronger than normal over the entire Atlantic basin for the remainder of the hurricane season.

Additionally, an abundance of dry air should make it harder for storms to spin up, as was the case this week when a tropical wave near Africa fell apart, said Jeff Masters, chief meteorologist of Weather Underground, an online weather site.

"Like last year, the tropical Atlantic and Caribbean continue to be dominated by high pressure and dry, sinking air, which discourages tropical storm formation," he said.

Because of these tropically hostile conditions, the National Oceanic and Atmospheric Administration calls for one to four hurricanes to emerge between now and Nov. 30 — on average it would be five hurricanes.

Just the same, forecasters urge residents to remain alert, particularly for the next three months.

"Tropical storms and hurricanes can strike the United States during below-normal seasons, as we have already seen this year when Arthur made landfall in North Carolina as a Category 2 hurricane," said Gerry Bell, NOAA's lead hurricane forecaster.

The problem is that conditions can change in short order and give tropical systems a window to grow, said James Franklin, top hurricane specialist at the National Hurricane Center.

"We're certainly not expecting a big season. But Andrew appeared at the end of August in a quiet season," he said, referring to the Category 5 hurricane that devastated south Miami-Dade County in 1992.

On average, about 80 percent of tropical activity occurs during August, September and October. The U.S. coastline has been struck most often in September with 74 hurricane hits since 1900, compared with 52 in August and 31 in October.

Yet South Florida is most vulnerable during October, as that's when storms are more likely to develop in the Caribbean and the Gulf of Mexico, and both are close to this area.

Consider that 19 hurricanes have struck this region in October, compared with 15 in September and 11 in August since tropical records started in 1851. Among the October systems: Hurricane Wilma in 2005, Hurricane Irene in 1999, Hurricane Isbell in 1964 and Hurricane King in 1950.

So far, Florida and the East Coast have benefited from an area of low-pressure over the eastern United States that has guided systems out to sea, including Hurricane Bertha earlier this month.

"Obviously, there is no guarantee that this pattern will continue," said Phil Klotzbach, the Colorado State University climatologist who develops seasonal forecasts.

With the busiest stretch of the hurricane season fast approaching, government forecasters slightly lowered their outlook on Thursday, now calling for seven to 12 named storms, including three to six hurricanes, with zero to two of those being major.